クリーンな環境でPesterによるテスト実行 (Original: Ensuring a Clean PowerShell Session for Your Pester Tests / https://mcpmag.com/articles/2018/02/01/clean-powershell-session-for-pester.aspx )

StartPester.ps1

function InvokePowerShellCommand
{
    [CmdletBinding()]
    param
    (
        [Parameter()]
        [ValidateNotNullOrEmpty()]
        [string]$Command
    )
    
    $Command | powershell.exe -NoProfile -NonInteractive -NoLogo -ExecutionPolicy Bypass -Command -
}

function ConvertTo-String
{
    [OutputType([string])]
    [CmdletBinding()]
    param
    (
        [Parameter(Mandatory)]
        [ValidateNotNullOrEmpty()]
        [hashtable]$Hashtable
    )
    $arr = $Hashtable.GetEnumerator().foreach({
        if ($_.Value -is 'hashtable') {
            "'$($_.Key)' = $(ConvertTo-String -HashTable $_.Value)"
        } else {
            "'$($_.Key)' = '$($_.Value)'"
        }
    })
    '@{{ {0} }}' -f ($arr -join ';')
}

function ConvertHashTableParametersToString
{
    [OutputType([string])]
    [CmdletBinding()]
    param
    (
        [Parameter()]
        [ValidateNotNullOrEmpty()]
        [hashtable]$Parameters
    )
    $Parameters.GetEnumerator().foreach({
        $paramName = $_.Key
        
        if ($_.Value -is [System.Management.Automation.SwitchParameter]) {
          if ($_.Value) {
            '-{0}' -f $paramName
          }
        }
        else {
          if ($_.Value -is 'hashtable') {
              $paramValue = ConvertTo-String -HashTable $_.Value
          } 
          else {
              $paramValue = '"{0}"' -f (@($_.Value) -join '","')
          }

          '-{0} {1}' -f $paramName,$paramValue
        }
    })
}

function Start-Pester
{
    [CmdletBinding()]
    param(
        [Parameter()]
        [ValidateNotNullOrEmpty()]
        [string]$Path,
        [switch]$PassThru,
        [switch]$Quiet
    )

    $invPesterParams = @{
        Path = $Path
        Show = if (-not $Quiet) { "All" } else { 'Fails' } 
        PassThru = $PassThru
    }

    ## Can't splat here because we're passing to another powershell.exe process
    $invPesterParamString = ConvertHashTableParametersToString -Parameters $invPesterParams
    
    $command = "Invoke-Pester $invPesterParamString "
    if (-not $PassThru) {
      InvokePowerShellCommand -Command $command
    }
    else {
      $log = New-TemporaryFile
      try {
        $output = InvokePowerShellCommand -Command ($command + " | Export-CliXml -Encoding utf8 $($log.FullName)")
        
        Import-CliXml $log
      }
      finally {
        Remove-Item $log
      }
    }
}